Often, electrical devices require the conversion of a DC voltage to an AC voltage. This function is referred to as the inversion of an electrical voltage and has previously been performed using several circuit topologies.
A first prior art circuit topology used to invert an electrical voltage is the push/pull circuit shown in FIG. 1. A DC source 13 (with optional filter capacitor 15 connected in parallel thereto) provides the DC voltage to be inverted. Two switches, 17 and 19 connect at a common node and to respective ends of a tapped transformer secondary 12. The center tap of secondary 12 connects to one terminal of DC source 13, with the other terminal of DC source 13 connecting to the common connection between the switches.
Operationally, alternate engagement of the switches 17 and 19 result in the generation of AC voltage at secondary 10. This topology has the disadvantage of the voltage on the switches being unclamped, and current only flowing in one of the two half-windings at a time.
Another prior art topology for an inverter circuit showing in FIG. 2, and is commonly understood to be the full-bridge type circuit. In this topology, again, a voltage source V.sub.IN 13 is connected in parallel with an optional filter capacitor 15 and provides the DC input for the circuit. In parallel with the DC input are two pairs of series connected switches, namely the series combination of SW.sub.3 27 and SW.sub.4 29 and the series combination of SW.sub.1 23 and SW.sub.2 25. A primary 14 of transformer 21 connects center nodes between the pairs of switches. The AC output is produced on a secondary 10 of transformer 21.
Operationally, the pairs of switches alternately engage, that is, SW.sub.1 23 and SW.sub.4 29 are simultaneously closed, and then the next switch pair, SW.sub.2 25 and SW.sub.3 27 are closed. This alternate engagement of the switches results in the AC voltage being generated on secondary 10. The full-bridge topology has the disadvantage of requiring the use of four switches, two of whom must conduct in series at any time, thereby resulting in complexity and additional switching losses.
Turning lastly to the prior-art half-bridge topology of FIG. 3, again a DC source V.sub.N 13 provides the DC input which is connected in parallel with a series combination of capacitors 37 and 39 and a series combination of switches SW.sub.1 31 and SW.sub.2 33. A transformer 35 has a primary 14 connected between a center node of the two series combinations of capacitors and switches, with transformer secondary 10 providing the AC output. Alternate operation of switches SW.sub.1 and SW.sub.2 result in the generation of the AC voltage output.
The half-bridge topology has the disadvantage of only applying one-half of the input voltage to the primary of the transformer at any given time.
Accordingly, the present invention is directed toward inversion circuits (and corresponding rectification circuits) which overcome the above-discussed defficiencies in the prior art.